distro: allow distro to specify a default locale

Currently the cloud-init default locale (en_US.UTF-8) is set by
the base datasource class.  This patch allows a distro to overide
the fallback value with one that's available in the distro but continues
to respect an image which has preconfigured a locale.

- Distro object now has a get_locale method which will return a
  preconfigure locale setting by checking the distros locale system
  configuration file.  If not set or not present, return the default
  locale of en_US.UTF-8 which retains behavior of all previous cloud-init
  releases.
- Apply locale now handles regenerating locales or system configuration
  files as needed.
- Adjust apply_locale logic to skip locale-regen if the specified LANG
  value is C.UTF-8,C, or POSIX; they do not require regeneration.
- Further add unittests to exercise the default paths for Ubuntu and
  non-ubuntu paths to validate they get the LANG expected.

2 files changed, 74 insertions, 23 deletions

diff --git a/cloudinit/distros/__init__.py b/cloudinit/distros/__init__.py
index 807b3ea2..b714b9ab 100755
--- a/cloudinit/distros/__init__.py
+++ b/cloudinit/distros/__init__.py
@@ -188,6 +188,9 @@ class Distro(object):
     def _get_localhost_ip(self):
         return "127.0.0.1"
 
+    def get_locale(self):
+        raise NotImplementedError()
+
     @abc.abstractmethod
     def _read_hostname(self, filename, default=None):
         raise NotImplementedError()
diff --git a/cloudinit/distros/debian.py b/cloudinit/distros/debian.py
index abfb81f4..33cc0bf1 100644
--- a/cloudinit/distros/debian.py
+++ b/cloudinit/distros/debian.py
@@ -61,11 +61,49 @@ class Distro(distros.Distro):
         # should only happen say once per instance...)
         self._runner = helpers.Runners(paths)
         self.osfamily = 'debian'
+        self.default_locale = 'en_US.UTF-8'
+        self.system_locale = None
 
-    def apply_locale(self, locale, out_fn=None):
+    def get_locale(self):
+        """Return the default locale if set, else use default locale"""
+
+        # read system locale value
+        if not self.system_locale:
+            self.system_locale = read_system_locale()
+
+        # Return system_locale setting if valid, else use default locale
+        return (self.system_locale if self.system_locale else
+                self.default_locale)
+
+    def apply_locale(self, locale, out_fn=None, keyname='LANG'):
+        """Apply specified locale to system, regenerate if specified locale
+            differs from system default."""
         if not out_fn:
             out_fn = LOCALE_CONF_FN
-        apply_locale(locale, out_fn)
+
+        if not locale:
+            raise ValueError('Failed to provide locale value.')
+
+        # Only call locale regeneration if needed
+        # Update system locale config with specified locale if needed
+        distro_locale = self.get_locale()
+        conf_fn_exists = os.path.exists(out_fn)
+        sys_locale_unset = False if self.system_locale else True
+        need_regen = (locale.lower() != distro_locale.lower() or
+                      not conf_fn_exists or sys_locale_unset)
+        need_conf = not conf_fn_exists or need_regen or sys_locale_unset
+
+        if need_regen:
+            regenerate_locale(locale, out_fn, keyname=keyname)
+        else:
+            LOG.debug(
+                "System has '%s=%s' requested '%s', skipping regeneration.",
+                keyname, self.system_locale, locale)
+
+        if need_conf:
+            update_locale_conf(locale, out_fn, keyname=keyname)
+            # once we've updated the system config, invalidate cache
+            self.system_locale = None
 
     def install_packages(self, pkglist):
         self.update_package_sources()
@@ -218,37 +256,47 @@ def _maybe_remove_legacy_eth0(path="/etc/network/interfaces.d/eth0.cfg"):
     LOG.warning(msg)
 
 
-def apply_locale(locale, sys_path=LOCALE_CONF_FN, keyname='LANG'):
-    """Apply the locale.
-
-    Run locale-gen for the provided locale and set the default
-    system variable `keyname` appropriately in the provided `sys_path`.
-
-    If sys_path indicates that `keyname` is already set to `locale`
-    then no changes will be made and locale-gen not called.
-    This allows images built with a locale already generated to not re-run
-    locale-gen which can be very heavy.
-    """
-    if not locale:
-        raise ValueError('Failed to provide locale value.')
-
+def read_system_locale(sys_path=LOCALE_CONF_FN, keyname='LANG'):
+    """Read system default locale setting, if present"""
+    sys_val = ""
     if not sys_path:
         raise ValueError('Invalid path: %s' % sys_path)
 
     if os.path.exists(sys_path):
         locale_content = util.load_file(sys_path)
-        # if LANG isn't present, regen
         sys_defaults = util.load_shell_content(locale_content)
         sys_val = sys_defaults.get(keyname, "")
-        if sys_val.lower() == locale.lower():
-            LOG.debug(
-                "System has '%s=%s' requested '%s', skipping regeneration.",
-                keyname, sys_val, locale)
-            return
 
-    util.subp(['locale-gen', locale], capture=False)
+    return sys_val
+
+
+def update_locale_conf(locale, sys_path, keyname='LANG'):
+    """Update system locale config"""
+    LOG.debug('Updating %s with locale setting %s=%s',
+              sys_path, keyname, locale)
     util.subp(
         ['update-locale', '--locale-file=' + sys_path,
          '%s=%s' % (keyname, locale)], capture=False)
 
+
+def regenerate_locale(locale, sys_path, keyname='LANG'):
+    """
+    Run locale-gen for the provided locale and set the default
+    system variable `keyname` appropriately in the provided `sys_path`.
+
+    """
+    # special case for locales which do not require regen
+    # % locale -a
+    # C
+    # C.UTF-8
+    # POSIX
+    if locale.lower() in ['c', 'c.utf-8', 'posix']:
+        LOG.debug('%s=%s does not require rengeneration', keyname, locale)
+        return
+
+    # finally, trigger regeneration
+    LOG.debug('Generating locales for %s', locale)
+    util.subp(['locale-gen', locale], capture=False)
+
+
 # vi: ts=4 expandtab